Fluid bearing motor, and disk drive mounted with same

ABSTRACT

The stop ring having a surface nearly vertical to the rotational center axis, which is projected at the inner periphery of the hollow cylinder of the rotor section, and the stepped surface of the fixed shaft secured on the chassis are opposed to each other with a predetermined slight clearance provided therebetween. The clearance is filled with magnetic fluid, and further, a permanent magnet is disposed on the chassis, opposing to the other surface of the stop ring.

FIELD OF THE INVENTION

The present invention relates to a fluid bearing motor used for amagnetic disk drive and an optical disk drive of a computer memory or apicture memory for recording/reproducing information at high densities,and a disk type recording/reproducing apparatus (hereinafter called diskdrive) mounted with the same.

BACKGROUND OF THE INVENTION

Recently, in the field of information recording/reproducing apparatusessuch as disk drive, efforts have been made to increase the capacity. Forincreasing the capacity, it is specially required to improve therotational accuracy of the spindle motor for driving the disk used inthe disk drive or the like. In order to meet the requirement forimproving the rotational accuracy, there is an increasing trend ofemploying a hydrodynamic bearing in the spindle motor.

In a hydrodynamic bearing, there exists a hydrodynamic lubricant betweena rotary side bearing and a fixed side bearing. The rotary side bearingand the fixed side bearing are provided with a dynamic pressuregenerating groove for inducing dynamic pressures to the hydrodynamiclubricant, which rotate the rotary body of the spindle motor via thehydrodynamic lubricant. That is, the spindle motor rotates in a state ofbeing non-contact between the rotary side bearing and the fixed sidebearing.

Thus, since the spindle motor rotates in a state of being non-contact,when a shock due to dropping or vibrating is applied thereto, the rotaryside bearing or the rotary body moves from the fixed side bearing. Incase the device is not configured so as to regulate the movement, therotary body will slip off from the fixed side bearing. This means thatthe spindle motor is unable to display its function.

Accordingly, a slip-proof configuration is adopted in order to preventthe rotary body from slipping off from the fixed side bearing even whena shock due to dropping or vibrating is applied thereto.

A slip-proof configuration of a conventional fluid bearing motor will bedescribed in the following.

As a fluid bearing motor, available are a fixed-shaft type and arotary-shaft type.

In the fixed-shaft type, the fixed side bearing is a fixed shaftembedded in a chassis. The rotary side bearing is rotatable around thefixed shaft.

In the rotary-shaft type, the rotary side bearing is rotatably supportedat the inner periphery of a cylindrical sleeve-like fixed side bearingfixed on a chassis.

First, the fixed-shaft type fluid bearing motor disclosed in JapaneseLaid-open Patent H6-311695 is explained.

In this prior art example, a generally cylindrical fixed shaft isdisposed upright. At the top of the fixed shaft is integrally formed anannular thrust plate projecting axially outwardly. On the other hand,the sleeve member which is a part of the rotary body is generallycylindrical which is increased in outer diameter at the top end. Theinner periphery of the sleeve member includes a radial slide portionbeing generally cylindrical with a small diameter, a medium bore portionincreased in diameter there above, and a large bore portion furtherincreased in diameter above the medium bore portion.

The sleeve member is externally fitted on a fixed shaft from thereunderbefore the fixed shaft is securely set into a through-hole. An annularthrust holding plate is internally secured in a state such that theinner periphery is diametrically spaced apart against the fixed shaft inthe large bore portion of the sleeve member. And, by the thrust holdingplate and the sleeve member, a thrust plate is fitted in the annularrecess of an opening diametrically outwardly formed at the inner side ofthe medium bore portion.

There is provided a herringbone groove at the annular portion of nearlythe upper half of the radial slide portion of the sleeve member. Aradial dynamic bearing is configured in that radial load pressures aregenerated by a liquid lubricant filled in the gap between theherringbone groove and the fixed shaft portion (radial receiver)opposing to the radial slide portion of the sleeve member.

Also, the upper and lower annular surfaces (axial receiver) of thethrust plate and the upper and lower annular surfaces (axial slide) ofthe annular recess respectively configure axial dynamic bearingportions. Herringbone grooves are formed along the entire peripheries ofthe upper and lower annular surfaces of the thrust plate, and highpressures are generated by the lubricant filled between the upper andlower annular surfaces of the annular groove, thereby forming an axialdynamic bearing portion.

In this way, it is configured in that the sleeve member or the like isable to freely rotate about the fixed shaft or the like via a lubricant.And, the displacement in a direction axial to the fixed shaft duringrotation of the sleeve member can be sufficiently lessened by the axialdynamic bearing portions. Accordingly, even in case a shock is appliedthereto, the sleeve member being a part of the rotary body will not slipoff from the fixed shaft being a fixed side bearing.

Next, the shaft-fixed type fluid bearing motor disclosed in JapaneseLaid-open Paten 2002-286038 is explained in the following.

In this prior art example, a shaft is externally fixed in a bracket.And, there are provided a disk-like upper thrust plate and lower thrustplate projected radially outwardly at the upper end and lower end of theshaft. There is a rotor which is provided with a sleeve supported by ashaft at the inner side thereof via a fine clearance for holding thelubricant. The sleeve is provided with an upper counter plate and lowercounter plate in such manner as to cover the outsides of the upperthrust plate and the lower thrust plate. The upper and lower portions atthe inner periphery of the through-hole of the sleeve are respectivelyformed with herringbone dynamic grooves by means of electrochemicalmachining. The underside of the upper thrust plate and the top of thelower thrust plate are respectively formed with spiral dynamic groovesby means of electrochemical machining. The portion ranging from theouter periphery of the shaft adjacent to the top of a gas-interveningportion disposed in the middle of the shaft to the underside of theupper thrust plate, the outer periphery thereof, and the outer peripheryof the top surface thereof is formed with fine clearances against theportion ranging from the top of the through-hole at the inner peripheryof the opposing sleeve to the underside of the upper counter plate,where the lubricant is retained.

In such a configuration, the radial dynamic bearing portion isconfigured with the upper and lower portions formed with the herringbonedynamic grooves at the inner periphery of the through-hole of thesleeve, the shaft opposing thereto, and the lubricant retained in thefine clearances. Also, the axial dynamic bearing is configured with (i)the underside of the upper thrust plate and the top of the lower thrustplate respectively formed with spiral dynamic grooves, (ii) theunderside of the upper counter plate and the top of the lower counterplate respectively opposing thereto, and (iii) the lubricant retained inthe fine clearances. The upper thrust plate and the lower thrust plateare held by the respective surfaces of the stepped portions of thesleeve respectively opposing to the underside of the upper thrust plateand the top of the lower thrust plate, and the underside of the uppercounter plate and the top of the lower counter plate disposed in suchmanner as to cover the outsides of the upper and lower thrust plates.

In such a configuration, the displacement in a direction axial to theshaft during rotation of the sleeve can be lessened enough. Accordingly,even in case a shock is applied thereto, the sleeve being a part of therotary body will not slip off from the shaft being the fixed sidebearing.

Next, the rotary-type fluid bearing motor disclosed in JapaneseLaid-open Patent H8-275447 is explained in the following.

In this prior art example, at the inner periphery of the cylindricalportion of a housing is disposed a sleeve having a projection at theouter periphery of the top end thereof. A motor rotates about a shaftfastened to the center of a rotor hub with a stopper fixed thereon. Athrust plate is caulked and secured to the bottom end of the sleevefixed on the inner periphery of the housing, in which lubricating oil isfilled as a fluid material. The thrust plate is formed with dynamicbearing grooves which are spiral grooves. The shaft is supported so asto be rotatable in a thrust direction due to dynamic pressure generatedat the thrust plate and the shaft end as it rotates. Simultaneously, theshaft is supported so as to be rotatable in a radial direction as welldue to dynamic pressure generated in the lubricating oil in a state ofbeing non-contact with the sleeve.

When the rotor hub moves in a thrust direction, the stopper fixed on therotor hub abuts the projection disposed at the sleeve. That is, it isconfigured in that the rotor hub will not slip off therefrom.

The motor assembling procedure is such that (i) a stator assembly with acoil-wound stator core fixed in a housing, (ii) a sleeve bearingassembly with a thrust plate fixed on a sleeve, and (iii) a rotorassembly with a shaft fixed on a rotor hub with a magnet arerespectively manufactured. Subsequently, lubricating oil is filled intothe sleeve of the sleeve bearing assembly, and the shaft of the rotorassembly is inserted to make a motor sub-assembly. In the condition ofthe motor sub-assembly, the stopper is secured to the rotor hub. Then,the stopper is in a state of being able to engage the projectiondisposed at the outer periphery of the top end of the sleeve fromthereunder. After that, the sleeve is inserted into the cylindricalportion of the housing of the stator assembly, thereby completing theassembling procedure.

Next, the rotary-shaft type fluid bearing motor disclosed in JapaneseLaid-open Patent H11-55900 is explained in the following.

In this prior art example, a hub fixed by a method of press-fitting to arotary shaft or the like is provided with a stop member made from amagnetic material. Further, an attracting magnet is fixed to the stopmember, which is opposed to a core of a coil assembly.

The bearing provided with a herringbone groove is a hydrodynamic bearingwhich supports the rotary shaft so as to be rotatable in a radialdirection, and a thrust plate supports the rotary shaft in an axialdirection.

In this configuration, even when a shock or vibration is applied to themotor, the rotary body is prevented from floating due to the attractiveforce generated between the attracting magnet and the coil assembly. Onthe other hand, even in case of excessive shocks, the rotary body isprevented from slipping off because it comes in slide contact with thebearing when moving in a thrust direction.

Next, the rotary-shaft type fluid bearing motor disclosed in JapaneseLaid-open Patent 2000-50567 is explained in the following.

In this prior art example, a rotor hub is provided with a stop plate forpreventing the rotor hub from slipping off. Also, a shaft is secured atthe center of the rotor hub, and a drive magnet is secured at the outerperiphery, thereby configuring a rotor section.

The shaft is rotatably inserted into the inner bore of a sleeve havingfirst and second cylindrical portions provided with herringbone groovesat the inner periphery thereof. And, a lubricating fluid is filled inthe clearance between the shaft and the sleeve, thereby configuring aradial hydrodynamic bearing. Also, one end of the shaft is sphericallyshaped, and a pivot bearing is formed by the spherical shape and athrust plate. And, a lubricating fluid is filled in the pivot bearingclearance, thereby configuring a thrust pivot bearing.

The method of assembling in the prior art example is explained in thefollowing. The thrust plate is caulked and fixed to the sleeve to make abearing assembly. Subsequently, a specified amount of lubricating oil isapplied to the inner periphery of the sleeve of the bearing assembly,and then, the shaft of a hub assembly having a rotor hub with amagnetized drive magnet bonded is inserted therein. A stop plate isfixed to the hub, and the stop plate prevents the bearing assembly fromslipping off. A predetermined amount of adhesive is applied to the innerperiphery of the internal cylindrical portion of a stator assembly,followed by inserting a sleeve with a rotor hub built in. The statorassembly is such that a coil assembly with a coil wound on a stator coreis secured by adhesive in a housing.

In this prior art example, the stop plate is caulked and fixed to therotor hub. A flange is formed at the end of the sleeve. Due to thisconfiguration, when the rotor hub moves in a thrust direction, theflange stops the stop plate, thereby preventing the rotor hub fromslipping off.

In the configuration of the above conventional fluid bearing motor, thefluid bearing motor must be assembled according to the procedure asfollows: (i) hydrodynamic lubricant is applied to the fixed sidebearing, (ii) the rotary body is inserted into the fixed side bearing tobe assembled, (iii) a member having a stopping function is fixed to therotary body, (iv) the rotary body is assembled in such manner as not toslip off from the fixed side bearing, and (v) after that, the fixed sidebearing is secured onto a substrate (or bracket, base member, housing)by press-fitting, bonding or other method.

In case the fluid bearing motor is assembled by such procedure, (i) withhydrodynamic lubricant (or lubricating agent, lubricating oil,lubricating fluid) filled in the assembly of the fixed side bearing andthe rotary body, a member having a stopping function is fitted to therotary body, and the fixed side bearing is secured on a substrate. Thatis, the assembling procedure includes complicated steps requiringcareful handling.

Also, the fixed side bearing and rotary body assembly filled withhydrodynamic lubricant is to be frequently handled during the assemblingwork. Accordingly, it may give rise to leaking or running of thehydrodynamic lubricant filled. And, it is difficult to retain thespecified amount of hydrodynamic lubricant. Further, the fixed sidebearing may abut or come into contact with the portion opposed to thefixed side bearing of the rotary body. In that case, there may arisescratches or slight bruises on any one of the fixed side bearing and theportion opposed to the fixed side bearing of the rotary body. As aresult, it gives trouble in the finished product after completion of theassembly.

Also, in the conventional shaft-fixed fluid bearing motor, there mayarise a problem of leaking or running of the hydrodynamic lubricantduring the assembling work or due to excessive shocks or other causes.Consequently, in case the hydrodynamic lubricant sticks to the topsurface of the thrust holding plate (or upper counter plate, lowercounter plate, cover plate), the hydrodynamic lubricant sticks to thesurface of the disk attached to the outer periphery of the rotary bodydue to the centrifugal force caused by rotation, and it may give damageto the recording medium formed on the surface of the disk.

Further, in the above reference for a rotary-shaft type fluid bearingmotor, nothing is mentioned about a cover of a fluid bearing motor ordisk drive. For the reduction in thickness of a disk drive, a cover isgenerally disposed close to a rotary body. In this case, there arises aproblem such that when the cover is strained due to an external forceapplied thereto, it comes in slide contact with the rotary body of thefluid bearing motor located near there, resulting in rotationalvariation of the fluid bearing motor.

SUMMARY OF THE INVENTION

The present invention is intended to solve the above problems.

The fluid bearing motor of the present invention comprises:

a fixed bearing member;

a rotary bearing member;

a hydrodynamic lubricant filled between the fixed bearing member and therotary bearing member;

a rotor section having a hollow cylinder in the middle thereof, a flangeformed at one end of the hollow cylinder, and a rotary magnet disposedon the flange;

a fixed shaft with one end fixed on a chassis, which passes through thehollow cylinder; and

a stator provided with a coil which generates a rotational force incooperation with the rotary magnet,

wherein the fixed bearing member is disposed on the chassis,

the fixed bearing member and the rotary bearing member configure abearing which rotatably supports the rotor section,

the bearing is arranged at a position apart from the fixed shaft,

the fixed shaft includes a small diameter portion and a large diameterportion,

the hollow cylinder is formed with a projection at a part of its innerperiphery, and

the projection is arranged such that it is positioned within thediameter of the large diameter portion of the fixed shaft and outsidethe small diameter portion.

Also, the fluid bearing motor of the present invention, having anotherconfiguration, comprises:

a fixed bearing member;

a rotary bearing member;

a hydrodynamic lubricant filled between the fixed bearing member and therotary bearing member;

a rotor section having a hollow cylinder in the middle thereof, a flangeformed at one end of the hollow cylinder, and a rotary magnet disposedat the flange;

a fixed shaft with one end fixed on a chassis, which passes through thehollow cylinder; and

a stator provided with a coil which generates a rotational force incooperation with the rotary magnet,

wherein the fixed bearing member is disposed on the chassis,

the fixed bearing member and the rotary bearing member configure abearing which rotatably supports the rotor section,

the bearing is arranged at a position apart from the fixed shaft,

the fixed bearing member comprises a first inner periphery and a secondinner periphery,

the first inner periphery is smaller in diameter than the second innerperiphery,

the hollow cylinder is formed with a projection at a part of its outerperiphery, and

the projection is arranged in such manner that it is positioned withinthe diameter of the second inner periphery of the fixed bearing memberand outside the first inner periphery.

The disk drive of the present invention comprises:

a fluid bearing motor described above or a fluid bearing motor havinganother configuration described above;

at least one disk with recording medium formed on the surface thereof,which is placed on the top of a flange;

a cover which abuts one end of a fixed shaft;

at least one signal conversion element for recording/reproducing signalsin the recording medium formed on the disk, and

at least one oscillating means for positioning the signal conversionelement to a specified track position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side sectional view showing the configuration of the mainsection of a fluid bearing motor of a disk drive in the preferredembodiment 1 of the present invention.

FIG. 2 is a plane sectional view showing the configuration of mainsection of a fluid bearing motor of a disk drive in the preferredembodiment 1 of the present invention.

FIG. 3 is a partly sectional view showing the configuration of thehydrodynamic lubricant reservoir of a fluid bearing motor of a diskdrive in the preferred embodiment 1 of the present invention.

FIG. 4 is a side sectional view showing the configuration of mainsection of another fluid bearing motor of a disk drive in the preferredembodiment 1 of the present invention.

FIG. 5 is a side sectional view showing the configuration of mainsection of a fluid bearing motor of an outer rotor motor type of a diskdrive in the preferred embodiment 1 of the present invention.

FIG. 6 is a side sectional view showing the configuration of the mainsection of a fluid bearing motor of a disk drive in the preferredembodiment 2 of the present invention.

FIG. 7 is a partly enlarged sectional view showing the configuration ofanother fluid bearing motor of a disk drive in the preferred embodiment2 of the present invention.

FIG. 8 is a partly enlarged sectional view showing the configuration ofanother fluid bearing motor of a disk drive in the preferred embodiment2 of the present invention.

FIG. 9 is a side sectional view showing the configuration of mainsection of a fluid bearing motor of a disk drive in the preferredembodiment 3 of the present invention.

FIG. 10 is a partly enlarged sectional view showing the configuration ofan another fluid bearing motor of a disk drive in the preferredembodiment 3 of the present invention.

FIG. 11 is a partly enlarged sectional view showing the configurationnear the rotary magnet of another fluid bearing motor of a disk drive inthe preferred embodiment 2 of the present invention.

FIG. 12 is a partly enlarged sectional view showing the configurationnear the stop ring of a fluid bearing motor of a disk drive in thepreferred embodiment 4 of the present invention.

FIG. 13 is a partly enlarged sectional view showing the configurationnear the stop ring of another fluid bearing motor of a disk drive in thepreferred embodiment 4 of the present invention.

FIG. 14 is a side sectional view describing the configuration of mainsection of a disk drive with a fluid bearing motor in the preferredembodiment 5 of the present invention.

FIG. 15 is a partly sectional view showing the vicinity of the bearingportion of a fluid bearing motor of a disk drive in the preferredembodiment 5 of the present invention.

FIG. 16 is a partly sectional view for describing the hydrodynamiclubricant reservoir in the preferred embodiment 5 of the presentinvention.

FIG. 17 is a side sectional view showing the configuration of mainsection of another fluid bearing motor of a disk drive in the preferredembodiment 5 of the present invention.

FIG. 18 is a schematic sectional view of main section of a fluid bearingmotor and a disk drive showing another example of the preferredembodiment 5 of the present invention.

FIG. 19 is a partly enlarged sectional view showing the configurationnear the stop ring of a fluid bearing motor of a disk drive in thepreferred embodiment 6 of the present invention.

FIG. 20 is a partly enlarged sectional view of a fluid bearing motorshowing another example in the preferred embodiment 6 of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiments of the present invention will be described inthe following with reference to the drawings.

(Preferred Embodiment 1)

FIG. 1 and FIG. 2 describe a fluid bearing motor and a disk drive in thepreferred embodiment 1 of the present invention.

FIG. 1 is a side sectional view showing the configuration of mainsection of a fluid bearing motor of a disk drive in the preferredembodiment 1 of the present invention. FIG. 2 is a plane sectional viewshowing the configuration of main section of a fluid bearing motor of adisk drive in the preferred embodiment 1 of the present invention. FIG.1 corresponds to the cross-section of the fluid bearing motor in thepreferred embodiment 1 of the present invention when it is cut at theplane including the rotational center axis along the B—B line of FIG. 2.FIG. 2 corresponds to the cross-section of the fluid bearing motor inthe preferred embodiment 1 of the present invention when it is cut alongthe A—A line of the FIG. 1.

In FIG. 1 and FIG. 2, rotor section 2 rotating around rotational center1 includes hollow cylinder 2 a and flange 2 b in the vicinity of therotational center 1. Also, at bottom end 2 d of outer periphery 2 c andflange 2 b of the hollow cylinder 2 a is formed a dynamic pressuregenerating groove where rotary side bearing 2 e configuring a fluidbearing is disposed. Also, on the underside of the outer periphery ofthe flange 2 b of the rotor section 2 is fixed rotary magnet 3magnetized by a plurality of magnetic poles by means of press-fitting,bonding or other method. The rotor section 2 and the rotary magnet 3comprises rotary body 4.

The bore diameter at the inner periphery of the hollow cylinder 2 a islarger at the flange 2 b (large bore portion) and smaller at a part(small bore portion) of chassis 5 at least. That is, the inner peripheryof the hollow cylinder 2 a is formed with a first stepped surface 2 f atthe boundary between the large bore portion and the small bore portion.The first stepped surface 2 f is generally vertical to the axialdirection of the rotational center 1.

Corresponding to rotary side bearing 2 e, fixed side bearing 6 is fixedon the chassis 5 by means of press-fitting, bonding, welding or otherwell-known method. Stator 9 includes coil 7 and stator core 8 and isfixed on chassis 5. Coil 7 is wound around each of the plurality ofmagnetic pole-tips of the stator 9. The inner periphery at the end ofthe plurality of magnetic pole-tips of the stator 9 is opposed to theouter periphery of the rotary magnet 3 fixed on the rotor section 2.

Fixed shaft 10 with its axis nearly aligned to the rotational center 1is spaced apart from the inner periphery of the hollow cylinder 2 a ofthe rotor section 2, and is secured on the chassis 5 by means ofpress-fitting, bonding or similar method. Shield plate 11 formagnetically shielding magnetic flux leaking from the stator 9 is fixedon the chassis 5. Fluid bearing motor 12 is configured in this way.

The fixed shaft 10 has a stepped-shaft shape such that its outerdiameter is smaller at the chassis 5 (small diameter portion) and thediameter at its outer periphery is larger at the opposite side (largediameter portion) of the chassis 5. At the chassis 5, the outer diameterof the fixed shaft 10 is smaller than the bore diameter of the hollowcylinder 2 a, and at the opposite side of the chassis 5, the outerdiameter of the fixed shaft 10 is smaller than the bore diameter at theflange 2 b of the hollow cylinder 2 a. The second stepped surface 10 aof the fixed shaft 10 which is formed at the boundary between the largediameter portion and the small diameter portion is nearly vertical tothe axial direction of the rotational center 1. The first steppedsurface 2 f and the second stepped surface 10 a is very slightly spacedapart from each other, opposing to each other.

Female thread 10 b is formed at the center of the end portion of thefixed shaft 10 at the opposite side of the chassis 5.

Between the rotary side bearing 2 e and the fixed side bearing 6opposing to each other is filled hydrodynamic lubricant 13 such as estertype synthetic oil. And, a radial fluid bearing is configured by theouter periphery 2 c of the hollow cylinder 2 a, the inner periphery 6 aof the fixed side bearing 6 opposing thereto, and the hydrodynamiclubricant 13. Also, a thrust fluid bearing is configured by the lowerend 2 d of the flange 2 b, the upper end 6 b of the fixed side bearing 6opposing thereto, and the hydrodynamic lubricant 13. The dynamicpressure generating groove of the radial fluid bearing is a herringbonegroove configured by well-known technology. The dynamic pressuregenerating groove of the thrust fluid bearing is, for example, spirallyshaped such that the hydrodynamic lubricant 13 is pumped up in thedirection toward the rotational center 1. In use of such shape, thehydrodynamic lubricant 13 will not run outside.

In the above description, the dynamic pressure generating groove isformed at the rotary side bearing 2 e of the rotor section 2, but thepresent invention is not limited to this configuration. It is preferablefor the radial fluid bearing to form the dynamic pressure generatinggroove at either one of the rotary side bearing 2 e and the fixed sidebearing 6, that is, at either one of the outer periphery 2 c of thehollow cylinder 2 a and the inner periphery 6 a of the fixed sidebearing 6 opposing thereto. It is preferable for the thrust fluidbearing to form the dynamic pressure generating groove at either one ofthe lower end 2 d of the flange 2 b and the upper end 6 b of the fixedside bearing 6 opposing thereto.

FIG. 3 shows the configuration of the hydrodynamic lubricant reservoirof a fluid bearing motor of a disk drive in the preferred embodiment 1of the present invention. Hydrodynamic lubricant reservoir 31 is formedin the vicinity of the lower side (chassis side) in the axial directionof the radial fluid bearing, and hydrodynamic lubricant reservoir 32 isformed at the outer diameter side in the radial direction of the thrustfluid bearing. Further, hydrodynamic lubricant reservoir 33 is formed ina position nearly opposed to the dynamic lubricant reservoir 31 in thevicinity of the lower side (chassis side) in the axial direction of theradial fluid bearing, and hydrodynamic lubricant reservoir 34 is formedin a position nearly opposed to the hydrodynamic lubricant reservoir 32at the outer diameter in the radial direction of the thrust fluidbearing. In this configuration, the hydrodynamic lubricant 13 will notrun outside due to the action of surface tension or the like of thehydrodynamic lubricant 13 intervening in the range from the hydrodynamiclubricant reservoir 31 to the hydrodynamic lubricant reservoir 34.

The shape of the cross-section ranging from the hydrodynamic lubricantreservoir 31 to the hydrodynamic lubricant reservoir 34 is nearlytriangular in the figure, but the configuration is not limited to thisshape. Also, it is possible to omit the hydrodynamic lubricant reservoir33 and the hydrodynamic lubricant reservoir 34.

Next, the assembling procedure of the fluid bearing motor 12 in thepresent embodiment will be briefly described in the following.

The rotary magnet 3 is fixed on the rotor section 2 to make the rotarybody 4. The fixed side bearing 6, the stator 9 with coil 7 wound onstator core 8 and the shield plate 11 are respectively fixed in thepredetermined positions of the chassis 5 to make a chassis unit. Afterthe hydrodynamic lubricant 13 is applied (filled) in each dynamicpressure generating groove of the radial fluid bearing and the thrustfluid bearing, the rotary side bearing 2 e of the rotary body 4 isinserted into the fixed side bearing 6 of the chassis unit. After that,the clearance between the second stepped surface 10 a and the firststepped surface 2 f is managed so as to become a predetermined size, andthen the fixed shaft 10 is inserted into the hollow of the cylinder 2 aand is secured on the chassis 5 by means of press-fitting, bonding orwell-known method.

After assembling the motor 12, disk 14 with recording medium (not shown)formed thereon is placed on the top surface of the flange 2 b of therotor section 2. Disk holding member 16 having elasticity is secured onthe rotor section by means of screw 15, and thereby, the disk 14 issecured on the top surface of the flange 2 b.

Although it is not shown, a signal conversion element (such as amagnetic head and optical head) for recording/reproducing signals on therecording medium of the disk 14 is disposed opposite to the disk 14 viaan oscillating means (such as a suspension or optical pickup carrier)for positioning the element to a predetermined track position.

Also, the recording medium to be formed on the disk 14 is preferable tobe formed on both upper and lower sides of the disk 14. In this case,the signal conversion element and the oscillating means are configuredso as to correspond to the respective recording mediums formed on theupper and lower sides of the disk 14.

Next, the lower end of abutment 17 a of cover 17 is abutted on the upperend of the fixed shaft 10. And, the cover 17 is screwed to the femalethread 10 b of the fixed shaft 10 by means of set-screw 18 via thethrough-hole formed in the abutment. Further, the peripheral edge ofcover 17 is screwed to the chassis 5 or a casing (not shown). The diskdrive is configured by disk 14, the signal conversion element, theoscillating means, fluid bearing motor 12, and cover 17. Incidentally,the cover 17 and the fixed shaft 10 are not always necessary to bescrewed.

Even in case the cover 17 is pressed by some external force, since thetip end of the fixed shaft 10 is positioned higher than the end (the endof a portion nearest to the abutment 17 a of cover 17) of the uppermostend of the rotary portion of the rotor section 2 or rotary body 4, andalso the abutment 17 a of cover 17 is in contact with the tip end of thefixed shaft 10, the cover 17 will not come in slide contact with therotary portion of the fluid bearing motor 12. That is, it will notresult in rotational variation of the fluid bearing motor 12.

The clearance between the upper most end of the rotary body 4 and theabutment 17 a of cover 17 is greater than the clearance between thefirst stepped surface 2 f and the second stepped surface 10 a.

Also, the cover 17 is fastened to the fixed shaft 10 at the top centerof the fluid bearing motor 12, and thereby, the whole casing includingthe chassis 5 is improved in rigidity, making it possible to make theresonance point higher. As a result, the level of vibration generateddue to the rotation of the fluid bearing motor 12 or the like can beeffectively suppressed. Also, as the whole casing is improved inrigidity, even when excessive load such as dropping impact is applied tothe casing, it is possible to prevent the occurrence of permanentdeformation.

Also, since a magnetic material is used for the chassis 5, magneticattraction is generated between the rotary magnet 3 and the chassis 5opposed to the lower end thereof and between the stator 9 and the rotarymagnet 3.respectively. Thus, the rotor section 2 can be prevented fromfloating against normal vibration or shocks. When the magneticattraction between the rotary magnet 3 and the chassis 5 is excessive,the amount of floating is reduced by the thrust fluid bearing or it mayfail to float. However, the amount of floating of the rotor section 2due to rotation of the rotor section 2 can be maintained by providingshield plate 19 for adjusting the attraction on a surface opposing tothe chassis of rotary magnet 3.

Also, even in case of excessive vibration, dropping or other shocks, thefirst stepped surface 2 f comes in slide contact with the second steppedsurface 10 a, and then, the rotary side bearing 2 e or the rotor section2 will no slip off from the fixed side bearing 6.

Further, since the clearance between the first stepped surface 2 f ofthe hollow cylinder 2 a and the second stepped surface 10 a of the fixedshaft 10 is very slight, even when the first stepped surface 2 f comesin slide contact with the second stepped surface 10 a, the amount offloating (movement) of the rotor section 2 can be greatly reduced. Thatis, there arises no problem such that the disk 14 bumps excessivelyagainst the signal conversion element for recording/reproducing signalson the recording medium, causing the surface of disk 14 or the signalconversion element to be seriously damaged. Also, the oscillating meanswill not be seriously damaged.

Also, setting the fixed shaft 10 through the hollow of the hollowcylinder 2 a of the rotor section 2, the opposing portions of the lowerend 2 d of flange 2 b and the upper end 6 b of fixed side bearing 6becomes remote from the rotational center 1. As a result, it increasesin bearing rigidity as a thrust fluid bearing. Accordingly, the axiallength of the radial fluid bearing can be lessened, and the fluidbearing motor 12 and the disk drive can be reduced in thickness.

Also, in the preferred embodiment 1 described above, the fluid bearingmotor and the disk drive are loaded with one disk, but as shown in FIG.4, it is also possible to configure the fluid bearing motor 43 by awell-known method so that the rotor section 41 can be loaded with aplurality of disks 42.

In the preferred embodiment 1, a so-called radial gap inner rotor motoris described, but the present invention is not limited to thisconfiguration. It can be applied to the configuration of a so-calledradial gap outer rotor motor as well.

FIG. 5 is an example of radial gap outer rotor motor. In FIG. 5, sameelements and names as in FIG. 1 are given same reference numerals. Thestator 9 is fixed on the chassis 5 or on the chassis 5 via the fixedside bearing 6 in such manner that the outer periphery of stator 9 withcoil 7 wound on stator core 8 is opposed to the inner periphery of therotary magnet 3 fastened to the rotor section 2. The fixed shaft 10 isinserted into the hollow of the hollow cylinder 2 a of the rotor section2 with a clearance provided therebetween. The configuration in which apredetermined slight clearance is provided between the second steppedsurface 10 a of the fixed shaft 10 and the first stepped surface 2 f ofthe hollow cylinder 2 a of the rotor section 2 is identical with that ofthe preferred embodiment described above. The other configurations aresame as those of the above preferred embodiment, and the detaileddescription is omitted.

In the present preferred embodiment, as for the predetermined size ofclearance between the first stepped surface of the inner periphery ofthe hollow cylinder of the rotor section and the second stepped surfaceof the fixed shaft, it is necessary to make the clearance greater thanthe surface roughness based on the machining accuracy of the first andsecond stepped surfaces, and also, it is limited depending upon theproperty of the fluid filled therein. At the bearing of the fluidbearing motor in the present invention, it is desirable to set theclearance between the first and second stepped surfaces to a range from5 μm to 100 μm.

(Preferred Embodiment 2)

FIG. 6 is a side sectional view showing the configuration of mainsection of a fluid bearing motor of a disk drive in the preferredembodiment 2 of the present invention. It shows the cross-section of thefluid bearing motor cut at a plane including the rotational center axis.In FIG. 6, same elements and names as in FIG. 1 are given same referencenumerals.

In FIG. 6, the rotor section 2 rotating around the rotational center 1includes the hollow cylinder 2 a and flange 2 b in the vicinity ofrotational center 1. The outer periphery 2 c of hollow cylinder 2 a andthe lower end 2 d of flange 2 b are formed with dynamic pressuregenerating grooves, and with rotary side bearing 2 e that is a fluidbearing. The rotary magnet 3 magnetized by a plurality of magnetic polesis fixed on the underside of the outer periphery of flange 2 b by meansof press-fitting, bonding or other method. The rotary body 4 comprisesthe rotor section 2 and the rotary magnet 3.

In the present preferred embodiment, the shape of the inner periphery ofthe hollow cylinder 2 a is different from that in the preferredembodiment 1. As shown in the figure, projection 2 g is formedcorresponding to the small bore portion in the preferred embodiment 1.The projection 2 g is formed between the chassis 5 at the innerperiphery thereof and the flange 2 b. The bore diameter at flange 2 b ofthe hollow cylinder 2 a is larger than the bore diameter of projection 2g. Also, the bore diameter at chassis 5 of the hollow cylinder 2 a islarger than the bore diameter of projection 2 g and at least larger thanthe bore diameter at the flange 2 b. In this case, the surface at flange2 b of the flange side projection 2 g is the first stepped surface 2 h.Also, the lower stepped surface 2 i that is the surface at chassis 5 ofthe projection 2 g and the first stepped surface 2 h are nearly verticalto the axial direction of the rotational center 1.

Also, the same as in the preferred embodiment 1, (i) fixed side bearing6 corresponding to rotary side bearing 2 e of rotor section 2, (ii)stator 9 with coil 7 wound on stator core 8, opposing to the outerperiphery of rotary magnet 3, (iii) fixed shaft 10 having a steppedshaft shape, and (iv) shield plate 11 are fixed on chassis 5. On theother hand, permanent magnet 61 is fixed to the chassis 5 by means ofbonding or other method so as to be opposed to the lower stepped surface2 i of projection 2 g with a slight clearance provided therebetween. Thepermanent magnet 61 is disposed without coming in contact with the innerperiphery of the hollow cylinder 2 a. The fluid bearing motor 62 isconfigured as described above.

Instead of fixing the permanent magnet 61 to the chassis 5, as shown inthe partly enlarged sectional view of FIG. 7, it is also preferable tobe fixed on the lower stepped surface 2 i of projection 2 g.

The fixed shaft 10 is secured on the chassis 5 in such manner that thesecond stepped surface 0a is opposed to the first stepped surface 2 h ofprojection 2 g with a very small predetermined clearance 63 providedtherebetween. The predetermined clearance 63 is filled (supplied) withmagnetic fluid containing, for example, synthetic oil of hydrocarbon orester type.

By using magnetic material as the rotor section 2 and fixed shaft 10, aclosed magnetic circuit is formed where the magnetic flux flows in theorder of (a) permanent magnet 61, (b) clearance between permanent magnet61 and lower stepped surface 2 i of projection 2 g, (c) projection 2 g,(d) clearance 63, (e) fixed shaft 10, (a) permanent magnet 61. Since aclosed magnetic circuit is formed in this way, the magnetic fluid filledin the clearance 63 is attracted. That is, the magnetic fluid is freefrom leaking, scattering, or running outside. Thus, it is preferable touse a magnetic material for the chassis 5 in order to form a closedmagnetic circuit.

Moreover, for example, the configuration of the fluid bearing andhydrodynamic lubricant reservoir and the assembling procedure areidentical with those in the preferred embodiment 1, and the descriptionis omitted here.

Also, another preferred embodiment is shown in FIG. 8. In FIG. 8, at theinner periphery of hollow cylinder 2 a is provided taper shape 81 nearthe projection 2 g at the flange 2 b. The taper shape 81 is largest indiameter at the upper stepped surface 2 h of the projection 2 g. Sincethe inner periphery of the hollow cylinder 2 a is thus configured, evenin case the magnetic fluid filled in clearance 63 drains to the topinner periphery from the projection 2 g for some reasons, the magneticfluid will move toward the projection 2 g along the tapered surface dueto rotationally centrifugal forces. That is, the drained magnetic fluidgathers near the top of the projection 2 g. Accordingly, the magneticfluid will not run out to the top along the inner periphery of thehollow cylinder 2 a, and naturally, the surface of disk 14 is notdamaged.

Also in the case of a fluid bearing motor in the preferred embodiment 2of the present invention, as to the predetermined size of clearancebetween the first stepped surface 2 h of projection 2 g and the secondstepped surface 10 a of the fixed shaft, it is necessary to make thesize larger than the surface roughness based on the machining accuracyof the upper stepped surface 2 h and the second stepped surface 10 a ofthe fixed shaft, and it is limited depending upon the property of thefluid filled therein. In the bearing of the fluid bearing motor in thepreferred embodiment 2 of the present invention, it is desirable to setthe clearance to a size ranging from 5 μm to 100 μm.

Further, the configuration of the disk drive comprising fluid bearingmotor 62 thus configured, disk 14, the signal conversion element, theoscillating means and cover 17 is identical with that of the preferredembodiment 1 described earlier. And, the configuration including fixedshaft 10 and cover 17 is also same as in the preferred embodiment 1.

Also, the configuration of a spindle motor in the preferred embodiment 2of the present invention is not limited to a so-called radial gap innerrotor motor. It can be applied to the configuration of a so-calledradial gap outer rotor motor as well the same as in the preferredembodiment 1, and the description is omitted here.

As described above, according to the present preferred embodiment, sameeffects as in the preferred embodiment 1 can be obtained. Further, evenwhen the rotor section is moved due to shocks or the like, causing thefirst stepped surface of the projection to come in slide contact withthe second stepped surface of the fixed shaft, the sliding friction isvery slight because of the magnetic material existing therebetween.Accordingly, the fluid bearing motor is free from generation ofrotational variation and able to maintain smooth rotation. Thus, it ispossible to realize a fluid bearing motor reduced in thickness which mayassure high shock resistance and excellent reliability

Also, using a fluid bearing motor having such a configuration in a diskdrive, it is possible to realize an excellent disk drive the same as inthe preferred embodiment 1.

(Preferred Embodiment 3)

FIG. 9 shows the configuration of main section of a fluid bearing motorof a disk drive in the preferred embodiment 3 of the present invention.The cross-section of the fluid bearing motor cut at a plane includingthe rotational center axis is shown in the figure. In FIG. 9, the sameelements and names as in FIG. 1 and FIG. 6 are given same referencenumerals.

In the present preferred embodiment, in place of projection 2 g in thepreferred embodiment 2, ring-form stop-ring 91 as a separate member isprovided at the inner periphery of hollow cylinder 2 a of rotor section2, and projection 91 b is formed.

Different points are mainly described in the following.

In FIG. 9, the inner periphery of hollow cylinder 2 a of rotor section 2configuring rotary body 4 is small in bore diameter at the flange 2 bside, and large in bore diameter at the chassis 5 side. The thirdstepped surface 2 j at the boundary between the small bore and the largebore is nearly vertical to the axial direction of the rotational center1.

The stop ring 91 formed of a ring-like magnetic material having top andbottom surfaces nearly vertical to the axial direction of the rotationalcenter 1 is fastened to the third stepped surface 2 j by means ofbonding, screwing or other well-known method in such manner that it isabutted on the third stepped surface 2 j. More specifically, projection91 a is formed by the stop ring 91 projected from the inner periphery ofthe hollow cylinder 2 a so that it is shaped same as the projection 2 g(see FIG. 6) in the preferred embodiment 2.

The bore diameter of stop ring 91 is smaller than the bore diameter ofhollow cylinder 2 a, and smaller than the large diameter of fixed shaft10 fixed on the chassis 5 and larger than the small diameter thereof.

In this case, the upper surface of the projection 91 a is the firststepped surface 91 b. The first stepped surface and the second steppedsurface 10 a of fixed shaft 10 are configured so as to be opposed toeach other with very small predetermined clearance 92 providedtherebetween. The clearance 92 is filled with magnetic fluid containing,for example, synthetic oil of hydrocarbon or ester type, the same as inthe preferred embodiment 2. Also, permanent magnet 61 is fixed on thechassis 5 so as to be opposed to the lower stepped surface 91 c ofprojection 91 a, the same as in the preferred embodiment 2. Since amagnetic material is used as the fixed shaft 10, a closed magneticcircuit is formed where the magnetic flux flows in the order of (a)permanent magnet 61, (b) stop ring 91 formed of a magnetic material, (c)fixed shaft 10, (a) permanent magnet 61. Since a closed magnetic circuitis formed in this way, the magnetic fluid is free from leaking,scattering or running.

The same as in the preferred embodiment 2, the permanent magnet 61 isnot fixed on the chassis 5, but as shown in the partly enlargedsectional view of FIG. 10, it is preferable to fasten the magnet to thelower stepped surface 91 c at the lower part of the stop ring 91.

Also, since a magnetic material is used as the chassis 5, a closedmagnetic circuit can be efficiently formed, the same as in the preferredembodiment 2.

Also, the clearance 92 between the first stepped surface 91 b and thesecond stepped surface 10 a is very slight, and making the clearancebetween the inner periphery of the projection 91 a and the outerperiphery of the fixed shaft 10 opposing thereto larger than theclearance 92, the stop ring 91 is not always necessary to be a magneticmaterial

Further, it is of course preferable to integrate the stop ring 91 andthe permanent magnet 61, forming a permanent magnet to be used as a stopring.

Also, FIG. 11 shows a partly enlarged sectional view in the vicinity ofrotary magnet 3. The rotary magnet 3 is fixed on back yoke 111 made froma magnetic material by means of bonding or the like, which is thenfastened to the underside of flange 2 b of rotor section 2. In thisconfiguration, a non-magnetic material of small specific gravity such asaluminum or resin can be used for the manufacture of the rotor section2. Since the mass of the rotor section 2 is reduced, it is possible tomake the rotor section 2 hard to move against vibrations, shocks or thelike. Also, since the stop ring 91 is made from a magnetic material, aclosed magnetic circuit is formed where the magnetic flux flows in theorder of (a) permanent magnet 61, (b) stop ring 91, (c) fixed shaft 10,(d) chassis 5, and (a) permanent magnet 61. Accordingly, it is possibleto prevent scattering or running of the magnetic fluid the same asdescribed above.

The configuration as a fluid bearing motor and the configuration as adisk drive are same as in the preferred embodiment 2, and thedescription is omitted here.

Also, the configuration of a spindle motor in the preferred embodiment 3of the present invent ion is not limited to a so-called radial gap innerrotor motor. It can be applied to the configuration of a so-calledradial gap outer rotor motor, the same as in the preferred embodiment 1and the preferred embodiment 2, and the description is omitted here.

As described above, according to the present preferred embodiment, sameeffects as in the preferred embodiment 1 and the preferred embodiment 2can be obtained. That is, even in case of excessive vibration, droppingor other shocks, the first stepped surface 91 b comes in slide contactwith the second stepped surface 10 a, and the rotor section will notslip off from the fixed side bearing. Also, due to the magnetic fluidfilled between the first stepped surface 91 b and the second steppedsurface 10 a, the rotational variation of the fluid bearing motor can besuppressed when the first stepped surface 91 b comes in slide contactwith the second stepped surface 10 a. Further, the assembling procedureis very simple, and it is possible to realize a fluid bearing motorreduced in thickness and most suited for a disk drive, which may assurehigh shock resistance and excellent reliability.

As for the fluid bearing motor in the preferred embodiment 3 of thepresent invention, the predetermined size of clearance between the firststepped surface 91 b and the second stepped surface 10 a is necessary tobe greater than the surface roughness based on the machining accuracy ofthe first and second stepped surfaces or the magnetic fine particles ofmagnetic fluid, and also, it is limited depending upon the property ofthe fluid filled therein. At the bearing of the fluid bearing motor inthe preferred embodiment 3 of the present invention, it is desirable toset the clearance to a size ranging from 5 μm to 100 μm.

Also, using a fluid bearing motor having such a configuration in a diskdrive, the disk and the signal conversion element can be prevented fromexcessively bumping against each other. Accordingly, the recordingmedium formed on the disk surface, the signal conversion element, or theoscillating means for positioning the signal conversion element will notbe seriously damaged. Also, the fluid bearing motor is free fromrotational vibration due to shocks or other causes that may result inserious damage to the information recording/reproducing operation, andit is possible to realize a thin disk drive which may assure high shockresistance.

(Preferred Embodiment 4)

FIG. 12 is a partly enlarged sectional view showing the configurationnear the stop ring of a fluid bearing motor of a disk drive in thepreferred embodiment 4 of the present invention. FIG. 13 is a partlyenlarged sectional view showing the configuration near the stop ring ofa fluid bearing motor of another disk drive in the preferred embodiment4 of the present invention. In FIG. 12 and FIG. 13, the same elements asin FIG. 1 and FIG. 9 described above are given same reference numerals.

In FIG. 12, (i) the third stepped surface 2 j of hollow cylinder 2 a isshaped nearly vertical to the axial direction of rotational center 1,(ii) to form projection 121 a, ring-form stop ring 121 is abutted on thethird stepped surface 2 j so as to be nearly vertical to the axialdirection of the rotational center 1, (iii) the first stepped surface121 b at the upper part of the projection 121 a of the stop ring 121 isopposed to the second stepped surface 10 a of the fixed shaft 10 withvery slight predetermined clearance provided therebetween, the same asin the preferred embodiment 3 described above.

The differences from the preferred embodiment 3 are such that (i) thematerial for stop ring 121 is a resin material having low frictioncharacteristics such as polyacetal resin, (ii) no magnetic fluid isfilled between the first stepped surface 121 b and the second steppedsurface 10 a, and (iii) there is provided no permanent magnet opposingto the lower stepped surface 121 c at the lower part of the stop ring121. The other configurations are identical with those in the preferredembodiment 3, and the description is omitted here.

In the above configuration, even when subjected to excessive vibrations,dropping or other shocks, the first stepped surface 121 b comes in slidecontact with the second stepped surface 10 a, and therefore, the rotorsection 2 will not slip off from the fixed side bearing 6. Also, using aresin material having low friction characteristics as the material forstop ring 121, the sliding friction is very much decreased as againstthe slide contact between the first stepped surface 121 b and the secondstepped surface 10 a, and it is possible to prevent the fluid bearingmotor from rotational variation caused by slide contact.

Also, in the configuration of FIG. 13, the stepped surface of steppedportion 2K is nearly vertical to the axial direction of rotationalcenter 1. In order to form projection 131 a so as to abut the steppedportion 2K by using a resin material having low friction characteristicssuch as polyacetal resin and in same dimensional relations as in thepreferred embodiment 3, stop ring 131 is secured by a well-know methodsuch as press-fitting, bonding or screwing. In this case, the firststepped surface 131 b, top surface of the stop ring 131, becomes nearlyvertical to the axial direction of the rotational center 1. And, thefirst stepped surface 131 b is opposed to the second stepped surface 10a of fixed shaft 10 with very slight predetermined clearance providedtherebetween. The other configurations are same as in the preferredembodiment 1, and the description is omitted here.

Same as in the configuration shown in FIG. 12, even when subjected toexcessive vibrations, dropping or other shocks, the rotor section 2 willnot slip off from the fixed side bearing 6. Also, the sliding frictionis very low as against the slide contact between the first steppedsurface 131 b and the second stepped surface 10 a, and it is possible toprevent the fluid bearing motor from rotational variation caused byslide contact.

In the fluid bearing motor in the present preferred embodiment 4 of thepresent invention, as for the predetermined size of clearance betweenthe first stepped surface 121 b (131 b) and the second stepped surface10 a, it is necessary to make the clearance greater than the surfaceroughness based on the machining accuracy of the stepped portion 2K, thefirst stepped surface 121 b (131 b) and second stepped surface 10 a, andalso, it is limited depending upon the property of the fluid filledtherein. At the bearing of the fluid bearing motor in the preferredembodiment 4 of the present invention, it is desirable to set theclearance to a size ranging from 5 μm to 100 μm.

Also, the configuration of the disk drive provided with a fluid bearingmotor thus configured, disk, signal conversion element, oscillatingmeans and cover is same as in the preferred embodiment 1, the preferredembodiment 2, and the preferred embodiment 3. Also, the configuration ofthe fixed shaft and cover is also same as in the preferred embodiment 1,the preferred embodiment 2, and the preferred embodiment 3.

Also, the configuration of the spindle motor in the preferred embodiment4 of the present invention is not limited to a so-called radial gapinner rotor motor. It can be applied to the configuration of a so-calledradial gap outer rotor motor as well the same as in the preferredembodiment 1, the preferred embodiment 2, and the preferred embodiment3, and the description is omitted here.

As described above, according to the present preferred embodiment, sameeffects as in the preferred embodiment 1, the preferred embodiment 2,and the preferred embodiment 3 can be obtained.

In the preferred embodiment 1 through the preferred embodiment 4, theconfiguration of a peripheral-opposed core attached motor is described,but the present invention is not limited to such configuration, and itis preferable to be the configuration of a plane-opposed core attachedmotor, and of course, the configuration of a coreless motor.

(Preferred Embodiment 5)

FIG. 14 is a side sectional view showing the configuration of mainsection of a disk drive of a fluid bearing motor in the preferredembodiment 5 of the present invention.

In FIG. 14, the rotary shaft 102, a hollow cylinder rotating around therotational center 101, is a hollow cylindrical shape having a steppedportion at its outer periphery. The stepped surface 102 a formed at theupper side (opposite to the chassis 103 side) of the rotary shaft 102and the outer periphery 102 c of the stepped surface 102 b formed at thelower side (the chassis 103 side) are formed with radial dynamicpressure generating grooves. The rotor unit 104 is secured so as to beabutted on the stepped surface 102 a and fitted on the outer peripheryof rotary shaft 102 above the stepped surface 102 a by a well-knownmethod such as press-fitting, bonding or the like. Rotor 105 comprisesthe rotary shaft 102 a and the rotor unit 104. The rotor 105 is notnecessary to be formed of individual members such as rotary shaft 102and rotor unit 104, but it is also preferable to be integrally formed.The ring-form stop ring 106 is secured so as to be abutted on thestepped surface 102 b and fitted on the outer periphery of the rotaryshaft 102 below the stepped surface 102 b by a well-known method such aspress-fitting, screwing or caulking. The stop ring 106 is preferable tobe formed of a metallic material or a resin material having low frictioncharacteristics. The rotor unit 104 has flange 104 a, and the underside104 b of the flange 104 a is formed with a thrust dynamic pressuregenerating groove. Also, the rotary magnet 107 magnetized by a pluralityof magnetic poles is fixed on the underside (chassis 103 side) at theouter periphery of the flange 104 a by press-fitting, bonding or othermethod. Rotary body 108 comprises the rotary shaft 102, rotor unit 104,stop ring 106 and rotary magnet 107.

The fixed side bearing 109 opposed to each of the outer periphery 102 cand the flange 104 a via a small clearance is secured on the chassis 103by bonding, screwing or other well-known method.

The fixed side bearing 109 has two inner peripheries different in borediameter. And, the first inner periphery 109 a smaller in bore diameterof the fixed side bearing 109 is opposed to the second outer periphery102 c of the rotary shaft 102 via a small clearance. Also, the steppedsurface 109 c that is the boundary between the first inner periphery 109a of the fixed side bearing 109 and the second inner periphery 109 blarger in bore diameter is opposed to the top surface of the stop ring106 via a small clearance. The stepped surface 109 c is nearlyright-angled to the center axis of the fixed side bearing. And, thesecond inner periphery 109 b is opposed to the outer periphery of thestop ring 106.

The chassis 103 has positioning projection 103 a for positioning thefixed side bearing 109. At the inner periphery of the positioningprojection 103 a, the outer periphery of the chassis 103 of the fixedside bearing 109 is fitted on the inner periphery of the positioningprojection 103 a. The positioning projection is preferable to bering-form or at least three cylinders configured on the samecircumference.

FIG. 15 corresponds to the cross-section along the A—A line shown inFIG. 14. As shown in FIG. 15, in the present embodiment, there areprovided at least three cylindrical positioning projections 103 a. Also,the shape of each positioning projection 103 a is not limited to acylindrical shape at all. It is preferable provided that a part of theouter periphery of the positioning projection 103 a is in externalcontact with the outer periphery near the chassis 103 of the fixed sidebearing 109. Using the positioning projection 103 a thus formed as apositioning guide, the fixed side bearing 109 is secured on the chassis103.

The stator 112 is formed of coil 110 and stator core 211, and is fixedon the chassis 103. The coil 110 is wound on a plurality of magneticpole-tips of the stator 112. The inner periphery at the end of theplurality of magnetic pole-tips of the stator 112 is opposed to theouter periphery of the rotary magnet 107 fixed on the rotor unit 104.The fixed shaft 113 is nearly axially aligned to the rotational center1, and inserted into the hollow of the rotary shaft 102 with clearanceprovided therebetween, and is fixed on the chassis 103 by a well-knownmethod such as press-fitting or bonding. Also, the fixed shaft 113 isformed with a female thread at the center of the end portion opposite tothe chassis side. Shield plate 114 for shielding the magnetic fluxleaking from the stator 112 is secured on the chassis 103. Fluid bearingmotor 15 is configured in this way.

Between the outer periphery 102 c of rotary shaft 102 and the firstinner periphery 109 a of fixed side bearing 109, and between theunderside 104 b of flange 104 a and the top end of fixed side bearing109 opposed thereto is filled, for example, hydrodynamic lubricant 116such as ester type synthetic oil. A radial fluid bearing is formed bythe outer periphery 102 c and the first inner periphery 109 a opposingto the surface thereof A thrust fluid bearing is formed by the underside104 b of flange 104 a and the upper end surface of fixed side bearing109 opposing thereto. The dynamic pressure generating groove of theradial fluid bearing is a herringbone groove formed by well-knowntechnology. The dynamic pressure generating groove of the thrust fluidbearing is, for example, spirally shaped such that the hydrodynamiclubricant 116 is pumped up in the direction toward the rotational center1. In use of such spiral shape, the hydrodynamic lubricant 116 will notrun outside.

The outer periphery 102 c of rotary shaft 102 is formed with a radialdynamic pressure generating groove, and the underside 104 b of flange104 a is formed with a thrust dynamic pressure generating groove in theabove description, but the present invention is not limited to theconfiguration. It is preferable to form a radial dynamic pressuregenerating groove at either the outer periphery 102 c of rotary shaft102 or the first inner periphery 109 a opposing thereto. And, it ispreferable to form a thrust dynamic pressure generating groove at eitherthe underside 104 b of flange 104 a or the top end surface of fixed sidebearing 109 opposing thereto.

The first inner periphery 109 a is vertically held with the underside104 b of flange 104 a and the top surface of stop ring 106. Accordingly,the rotor 105 rotationally floats due to the thrust fluid bearing. It isnecessary to set the clearance between the stepped surface 109 c and thetop surface of stop ring 106 to a size more than the amount of floating.

FIG. 16 is a partly sectional view showing a hydrodynamic lubricantreservoir in the present preferred embodiment.

As shown in FIG. 16, (i) hydrodynamic lubricant reservoir 231 is formedat the lower side (chassis 103 side) of the first inner periphery 109 aof fixed side bearing 109, (ii) hydrodynamic lubricant reservoir 232 isformed at the outer periphery of the upper end surface of fixed sidebearing 109, (iii) hydrodynamic lubricant reservoir 233 is formed at aposition at the lower part of the outer periphery 102 c of rotary shaft102, nearly opposing to the hydrodynamic lubricant reservoir 231, and(iv) the fourth hydrodynamic lubricant reservoir 234 is formed at theouter periphery of the underside 104 b of flange 104 a, nearly opposingto the hydrodynamic lubricant reservoir 232. The hydrodynamic lubricant116 of the hydrodynamic lubricant reservoir 231 through the hydrodynamiclubricant reservoir 234 will not run outside due to the action ofsurface tension or the like. The sectional shapes of the hydrodynamiclubricant reservoir 232 through the hydrodynamic lubricant reservoir 234are generally triangular in the figure, but the present invention is notlimited to the shapes at all. The hydrodynamic lubricant reservoir 233and the hydrodynamic lubricant reservoir 234 can be omitted.

Next, the outline of the assembling procedure of fluid bearing motor 115having such a configuration will be described in the following.

First, the rotor unit 104 is secured so as to be abutted on the steppedsurface 102 a at the upper side of rotary shaft 102 and fitted on theouter periphery above the stepped surface 102 a of rotary shaft 102 by awell-know method such as press-fitting or bonding. And, the rotarymagnet 107 is fixed on the underside at the outer periphery of flange104 a by press-fitting, bonding or other method, thereby forming arotary body sub-unit. It is preferable to fix the rotor unit 104 on therotary shaft 102 after fixing the rotary magnet 107 on the rotor unit104.

Subsequently, each dynamic pressure generating groove of the thrustfluid bearing and the radial fluid bearing is coated (supplied) with thehydrodynamic lubricant 116.

The fixed side shaft 109 is inserted opposite to the second outerperiphery 102 c of the rotary shaft 102.

Next, the stop ring 106 is abutted on the stepped surface 102 b ofrotary shaft 102, and is screwed to the stepped surface 102 b. Or, thestop ring 106 is fixed on the rotary shaft 102 by fitting it on theouter periphery under the stepped surface 102 b. Or, the stop ring 106is fixed on the rotary shaft 102 by caulking it at the end of the rotaryshaft 102.

The rotary body 108 comprising rotor 105, rotary magnet 107 and stopring 106, and the fixed side bearing 109 form a rotary body bearingunit.

On the other hand, the stator 112 formed of coil 110 and stator core 211is fixed on the chassis 103 in a predetermined position by bonding orother well-known method. And, the shield plate 114 is fixed on thechassis 103 in such manner as to cover the stator 112. Further, thefixed shaft 113 is secured on the chassis 103 in a predeterminedposition by a method such as press-fitting or bonding, thereby forming achassis sub-unit. It is preferable to fix the stator 112 and the shieldplate 114 on the chassis 103 after securing the fixed shaft 113.

Next, the fixed shaft 113 secured on the chassis 103 forming the chassissub-unit is set through the hollow of the rotary shaft 102 forming therotary body unit, and the fixed side bearing 109 is fixed on the chassis103 by screwing or bonding, regulating the fitting position by thepositioning projection 103 a. The fluid bearing motor 115 ismanufactured in this way.

Subsequently, the disk 117 with a recording medium layer (also calledrecording medium film, not shown) formed thereon is placed on the topsurface of the flange 104 a. The disk 117 is pressed and fixed on thetop surface of the flange 104 a, securing the elastic disk holdingmember 119 by means of screw 118.

Although it is not shown in the figure, a signal conversion element (forexample, magnetic head or optical head) for recording/reproducingsignals on the recording medium layer formed on the disk 117 is disposedopposite to the disk 117 via an oscillating means (for example,suspension or optical pickup carrier) for positioning to thepredetermined track position.

Also, the recording medium layer formed on the disk 117 is preferable tobe formed on both top and bottom surfaces of the disk 117. In this case,the signal conversion element and the oscillating means are respectivelyopposed to the recording medium layers formed on the top and bottomsurfaces of the disk 117.

Next, the lower end of abutment 120 a of the cover 120 is abutted on theupper end of fixed shaft 113. And, the cover 120 is screwed onto thefemale thread 113 a of fixed shaft 113 by means of set-screw 121 via thethrough-hole formed in the abutment 120 a. Further, the peripheral edgeof the cover 120 is screwed to the chassis 103 or a casing (not shown)or the like. A disk drive is configured, comprising the disk 117, signalconversion element, oscillating means, fluid bearing motor 115, andcover 120. The cover 120 and the fixed shaft 113 are just enough to beabutted, which are not always required to be screwed.

Even when the cover 120 is compressed by an external force, since thetip end of the fixed shaft 113 is set higher than the position of theuppermost end (the end nearest to the abutment 120 a of cover 120) ofthe rotary portion of the rotor 105 or rotary body 108, and the abutment120 a of cover 120 is abutted on the tip end of the fixed shaft 113, thecover 120 will not come in slide contact with the rotary portion of thefluid bearing motor 115. That is, the fluid bearing motor 115 is freefrom rotational variation.

The clearance between the uppermost end of the rotary body 108 and theabutment 120 a of cover 120 is greater than the clearance between thestepped surface 109 c and the top surface of the stop ring 106.

Also, since the cover 120 is secured on the fixed shaft 113 at the uppercenter of the fluid bearing motor 115, the whole casing including thechassis 103 is enhanced in rigidity, and it is possible to make theresonance point higher. As a result, the level of vibration generateddue to the rotation of the fluid bearing motor 115 or the like can beeffectively lowered. Also, as the whole casing is increased in rigidity,it is possible to prevent the occurrence of permanent deformation evenin case an excessive load such as dropping shock is applied to thecasing.

Further, using a magnetic material as chassis 103, an attractive forceis created between the rotary magnet 107 and the chassis 103 opposing tothe bottom end thereof. Also, since the central height of the statorcore 211 is lower than the central height of the rotary magnet 107, theattractive force acts to move the rotor 105 down to the lower (chassis103) side. In this way, floating of the rotor 105 can be suppressedagainst normal vibrations or shocks.

Also, even in case of excessive vibration, dropping or other shocks, thetop surface of the stop ring 106 comes in slide contact with the steppedsurface 109 c of the fixed side bearing 109, and the rotor 105 will notslip off from the fixed side bearing 109.

Further, since the clearance between the top surface of the stop ring106 and the stepped surface 109 c is very slight, even when the steppedsurface 109 c comes in slide contact with the top surface of the stopring 106, the amount of floating (movement) of the rotor 105 is veryslight. Accordingly, the signal conversion element forrecording/reproducing signals will not surface of the disk 117, and therecording medium or the signal conversion element will not be seriouslydamaged. Also, the oscillating means will not be seriously damaged.

Also, as the stop ring 106, a resin material having low frictioncharacteristics such as polyacetal resin for example is used, and evenwhen the stepped surface 109 c comes in slide contact with the topsurface of the stop ring 106 due to shocks or the like, the slidingfriction generated by the stepped surface 109 c and the top surface ofthe stop ring 106 is very slight. Accordingly, it is possible to preventthe fluid bearing motor 115 from rotational variation caused by slidecontact.

Further, the fixed shaft 113 is set through the hollow of the rotaryshaft 102, and thus, the portion where the underside 104 b of flange 104a of the thrust fluid bearing is opposed to the upper end of the fixedside bearing 109 becomes remote from the rotational center 1.Consequently, the thrust fluid bearing is increased in bearing rigidity.Accordingly, the bearing length of the radial fluid bearing can belessened, and the fluid bearing motor 115 and the disk drive can bereduced in thickness.

Also, in the present preferred embodiment 5, the fluid bearing motor 115and the disk drive loaded with one disk have been described, but asshown in FIG. 17, it is also possible to configure the fluid bearingmotor 143 in such manner that a plurality of disks 142 can be placed inthe rotor unit 141.

In the preferred embodiment 5, the description refers to a so-calledradial gap inner rotor motor, but the present invention is not limitedto this. It can be applied to the configuration of a so-called radialgap outer rotor motor as well.

FIG. 18 shows an example of radial gap outer rotor motor. In FIG. 18,the same elements and names as those in FIG. 14 are given same referencenumerals. Stator 156 is fixed on chassis 157 in such manner that theouter periphery of the stator 156 with coil 154 wound on stator core 155is opposed to the inner periphery of rotary magnet 153 fixed on rotorunit 152 of rotor 151. The configuration in which a predetermined smallclearance is provided between the stop ring 106 fixed on the rotaryshaft 102 and the stepped surface 109 c of fixed side bearing 109 issame as in the preferred embodiment shown in FIG. 14, and the detaileddescription is omitted here.

As to the predetermined size of clearance between the first steppedsurface 109 c of fixed side bearing 109 and the top surface of stop ring106, it is necessary to make the size larger than the surface roughnessbased on the machining accuracy of the upper stepped portion or thestepped surface, and it is limited depending upon the property of thefluid filled therein. In the bearing of the fluid bearing motor in thepresent invention, it is desirable to set the clearance to a sizeranging from 5 μm to 100 μm.

(Preferred Embodiment 6)

FIG. 19 is a partly enlarged sectional view showing the configurationnear the stop ring of a fluid bearing motor of a disk drive in thepreferred embodiment 6 of the present invention. The vicinity of thestop ring is enlarged, showing the cross-section at a plane includingthe rotational center axis of the fluid bearing motor. In FIG. 19, thesame elements and names as in FIG. 14 are given same reference numerals,and the description is not repeated here.

In FIG. 19, the shape and the configuration of the rotary shaft 102 andring-form stop ring 161 are same as in the preferred embodiment shown inFIG. 14. In the present preferred embodiment, the stop ring 161 is madefrom magnetic material. The configuration in which the top surface ofthe stop ring 161 is opposed to the stepped surface 109 c of fixed sidebearing 109 with a slight clearance provided therebetween is same as inthe preferred embodiment 5.

Ring-form permanent magnet 162 is secured on chassis 103 so as to beopposed to the underside at chassis 103 side of the stop ring 161.

Except that the stop ring 161 is formed of a magnetic material, and thepermanent magnet 162 is secured on the chassis 103 opposing to the stopring 161, the configuration is same as in the preferred embodiment 5,and the detailed description is omitted here.

In such a configuration, magnetic material is used for the rotary shaft102, chassis 103, and fixed side bearing 109. Also, as hydrodynamiclubricant 116 used for thrust fluid bearing and radial fluid bearing,magnetic fluid containing synthetic oil for example such as hydrocarbonor ester type is used. In this way, a closed magnetic circuit is formedwhere the magnetic flux flows in the order of (a) permanent magnet 162,(b) clearance between permanent magnet 162 and stop ring 161, (c) stopring 161, (d) slight clearance between stop ring 161 and stepped surface109 c, (e) fixed shaft bearing 109, (f) chassis 103, (a) permanentmagnet 162. Even in case the hydrodynamic lubricant 116 filled in theradial fluid bearing runs out to the top surface of stop ring 161 forsome reasons, the hydrodynamic lubricant 116 then drained will beadsorbed in the small clearance between the stop ring 106 and thestepped surface 109 c due to the magnetic attraction of the closedmagnetic circuit. Thus, forming a closed magnetic circuit, it ispossible to effectively prevent the hydrodynamic lubricant 116 fromleaking, scattering or running outside. Even when the rotary shaft 102,chassis 103 and stop ring 161 are not made from magnetic material, thepermanent magnet 162 attracts the magnetic fluid, preventing it fromrunning out.

Also, as to the assembling procedure, a rotary body bearing unit isformed, which comprises the rotary body 108 having rotor 105, rotarymagnet 107 and stop ring 161 made from magnetic material, and the fixedside bearing 109. And, a chassis sub-unit is formed by securing thestator 112, shield plate 114, fixed shaft 113, and permanent magnet 162on the chassis 103. Other than these are same as in the preferredembodiment 5, and the description is omitted here.

Also, another example of a fluid bearing motor equipped with a diskdrive in the preferred embodiment 6 is described in the following withreference to FIG. 20.

FIG. 20 is a partly enlarged sectional view showing the configurationnear the hydrodynamic lubricant reservoir of another fluid bearing motorequipped with a disk drive in the preferred embodiment 6 of the presentinvention. The vicinity of the hydrodynamic lubricant reservoir isenlarged in the figure, showing the cross-section at a plane includingthe rotational center axis of the fluid bearing motor.

In FIG. 20, the same elements and names as in FIG. 14, FIG. 16 and FIG.19 are given same reference numerals.

In FIG. 20, hydrodynamic lubricant reservoir 172 is formed near theouter periphery of the stepped surface 171 c of fixed side bearing 171opposed to the stop ring 161. Also, same as in FIG. 16, hydrodynamiclubricant reservoir 173 is formed near the outer periphery of the upperend surface of the fixed side bearing 171 opposed to the underside 104 bof flange 104 a. Further, hydrodynamic lubricant reservoir 174 is formednear the outer periphery of the underside 104 b of flange 104 a.

In the present preferred embodiment that differs from the preferredembodiment shown in FIG. 16, in place of the hydrodynamic lubricantreservoir 231, hydrodynamic lubricant reservoir 172 is formed at thestepped surface 171 c, and the hydrodynamic lubricant reservoir 233 isnot formed. The stepped surface 171 c is formed at right angles to thefirst inner periphery 171 a.

It is possible to omit the hydrodynamic lubricant reservoir 174 the sameas in the preferred embodiment 5.

The hydrodynamic lubricant 175 is filled into slight clearance rangingfrom the hydrodynamic lubricant reservoir 172 to the hydrodynamiclubricant reservoir 173. A thrust fluid bearing is formed by theunderside 104 b of flange 104 a and the upper end surface of the fixedside bearing 171. A radial fluid bearing is formed by the outerperiphery 102 c of rotary shaft 102 and the first inner periphery 171 aof fixed side bearing 171. As hydrodynamic lubricant 175, magnetic fluidincluding synthetic oil such as hydrocarbon or ester type is used thesame as in the preferred embodiment shown in FIG. 19.

As described above, except the position of the hydrodynamic lubricantreservoir 172 and such configuration that the range of hydrodynamiclubricant 175 filled reaches the clearance between the stop ring 161 andthe stepped surface 171 c of fixed side bearing 171, the configurationis same as in the preferred embodiment shown in FIG. 19, and thedescription is omitted here.

In this configuration, magnetic material is used for the rotary shaft102, chassis 103 and fixed side bearing 171, and further, magnetic fluidis used as the hydrodynamic lubricant 175. That is, a closed magneticcircuit is formed the same as in the preferred embodiment shown in FIG.19. Due to the magnetic attraction of the closed magnetic circuit, thehydrodynamic lubricant 175 is adsorbed into the clearance. That is, thehydrodynamic lubricant 175 will not leak, scatter or run out from theclearance between the stop ring 161 and the stepped surface 171 c offixed side bearing 171. The same as in the above preferred embodiment,the rotary shaft 102, chassis 103 and stop ring 161 are not alwaysrequired to be made from magnetic material. Also in this case, themagnetic fluid is adsorbed and maintained by the magnetic flux of thepermanent magnet 162.

Also, as to the assembling procedure of the fluid bearing motor havingsuch a configuration, except that the corresponding portion between thehydrodynamic lubricant reservoir 172 and the hydrodynamic lubricantreservoir 173 is coated (supplied) with the hydrodynamic lubricant 175,the configuration is same as in the above preferred embodiment, and thedescription is omitted here.

In the above preferred embodiment, the permanent magnet 162 is securedon the chassis 103 so as to be opposed to the stop ring 161 in thedescription, but it is also preferable to secure the permanent magnet162 on the underside (at chassis 103 side) of the stop ring 161 in suchmanner as to be opposed to the chassis 103.

As is obvious in the above description, in the present preferredembodiment, same effects as in the preferred embodiment 5 can beobtained, and also, the following effects can be obtained.

Since it is configured in that the stop ring 161 is opposed to thepermanent magnet 162 fixed on the chassis 103, magnetic attraction isgenerated between the stop ring 161 and the permanent magnet 162. Thatis, the rotor 105 mounted with the disk 117 is attracted toward thechassis 103, resulting in improvement of the vibration resistance. Also,As a closed magnetic circuit is formed, the hydrodynamic lubricant 116,175 that is magnetic fluid will not leak, scatter or run out. Further,the hydrodynamic lubricant reservoir 172 is disposed at the steppedsurface 171 c of the fixed side bearing 171, and the hydrodynamiclubricant 175 is provided between the stop ring 161 and the steppedsurface 171 c opposing thereto. As a result, even in case of excessivevibration, dropping or other shocks, causing the stop ring 161 to comein slide contact with the stepped surface 171 c, the sliding frictionthen caused by slide contact will be very slight. Accordingly, the fluidbearing motor is free from the generation of rotational variation andmay assure smooth rotation.

The present preferred embodiment can be applied to the configuration ofa so-called radial gap outer rotor motor, the same as in the preferredembodiment 5.

The disk drive comprises a fluid bearing motor having configuration asdescribed above, and a disk, signal conversion element (not shown),oscillating means (not shown), and cover, the same as in the preferredembodiment 5. Also, as to the fixed shaft and cover, the configurationis same as in the preferred embodiment 5.

Also, the same as in the preferred embodiment 5, even when subjected toexcessive vibration, dropping or other shocks, the rotary body will notslip off from the fixed side bearing. Further, the force acting to holdthe rotor mounted with a disk is great enough to improve the vibrationresistance. It is possible to realize a highly reliable fluid bearingmotor which is reduced in thickness, most suited for a disk drive, andmay assure excellent shock resistance.

Further, a hydrodynamic lubricant reservoir is disposed at the steppedsurface of the fixed side bearing, and a hydrodynamic lubricant isprovided between the stop ring and the stepped surface of the fixed sidebearing opposed thereto. Due to this configuration, even in case ofexcessive vibration, dropping or other shocks, causing the stop ring tocome in slide contact with the stepped surface of the fixed side bearingopposing thereto, the sliding friction then caused by slide contact willbe very slight. Accordingly, the fluid bearing motor is free from thegeneration of rotational variation and may assure smooth rotation.

In the fluid bearing motor in the present preferred embodiment 6, as forthe size of clearance between the top surface of stop ring 161 and thestepped surface 109 c, and between the top surface of stop ring 161 andthe stepped surface 171 c, it is necessary to make the clearance greaterthan the surface roughness based on the machining accuracy of thestepped portion or the stepped surface or the magnetic fine particle ofthe magnetic fluid, and it is limited depending upon the property of thefluid filled therein. At the bearing of the fluid bearing motor in thepresent invention, it is desirable to set the clearance to a sizeranging from 5 μm to 100 μm.

Also, the same as in the preferred embodiment 5, even when the cover iscompressed by an external force applied to the cover, the cover will notcome in slide contact with the rotary portion of the fluid bearingmotor. Also, excessive bumping of the disk against the signal conversionelement is suppressed, and the recording medium layer formed on the disksurface, the signal conversion element for recording/reproducingsignals, or the oscillating means for positioning the signal conversionelement will not be seriously damaged.

In the preferred embodiment 5 and the preferred embodiment 6, theconfiguration of a peripheral-opposed core attached motor is described,but the present invention is not limited to this configuration, and itis of course preferable to be a plane-opposed core attached motor or acoreless motor.

1. A fluid bearing motor comprising: a hollow cylinder passed throughvia axis of rotational center; a flange formed at one end of said hollowcylinder; a rotor section provided with a rotary magnet disposed onouter bottom of said flange; a rotary bearing member configured with anouter cylinder surface of said hollow cylinder and a bottom end of saidflange; a chassis; a generally cylindrical fixed bearing member securedto said chassis and configured with an inner cylinder surface supportingsaid hollow cylinder so as to be rotatable via a small first radialspace and a plane supporting an inner side bottom end of the flange soas to rotate in an axial direction at upper surface of said plane; ahydrodynamic lubricant filled between said fixed bearing member and saidrotary bearing member; a fixed shaft with one end fixed on the chassis,which passes through the hollow cylinder via a second radial space widerthan said first radial space; and a stator provided with a coil whichgenerates a rotational force in cooperation with the rotary magnet.
 2. Afluid bearing motor according to claim 1, wherein: said fixed shaftincludes a small diameter portion and a large diameter portion, thehollow cylinder is formed with a projection at a part of its innerperiphery, and the projection is arranged in such manner that it ispositioned within the diameter of the large diameter portion of thefixed shaft and outside the small diameter portion.
 3. The fluid bearingmotor of claim 2, wherein the projection is circular, having asmall-bore portion formed at the inner periphery of said hollowcylinder.
 4. The fluid bearing motor of claim 2, wherein a first steppedsurface formed by the small-bore portion at the inner periphery of saidhollow cylinder and a second stepped surface formed by thesmall-diameter portion at the outer periphery of said fixed shaft areopposed to each other with a predetermined clearance providedtherebetween.
 5. The fluid bearing motor of claim 2, wherein theprojection is formed of a stop ring, and one surface of said stop ringabuts a third stepped surface formed at the inner periphery of saidhollow cylinder.
 6. The fluid bearing motor of claim 5, wherein saidstop ring is made from a resin material having a low friction factor. 7.The fluid bearing motor of claim 5, wherein said fixed shaft is madefrom a magnetic material, and the clearance between the first steppedsurface and the second stepped surface is filled with magnetic fluid,and said stop ring is formed of a permanent magnet.
 8. The fluid bearingmotor of claim 5 or 6, wherein in the vicinity of the first steppedsurface, the inner periphery of said hollow cylinder is tapered toincrease in bore diameter as it approaches the projection.
 9. The fluidbearing motor of claim 2, 3, 4 or 5 wherein the predetermined clearancebetween the first stepped surface and the second stepped surface rangesfrom 5 μm to 100 μm.
 10. The fluid bearing motor of claim 2 or 5,wherein said fixed shaft is made from a magnetic material, the clearancebetween the first stepped surface and the second stepped surface isfilled with magnetic fluid, and a magnet is disposed on said chassis,opposing to the inner periphery of said hollow cylinder at the chassisside rather than the projection.
 11. The fluid bearing motor of claim10, wherein said stop ring is made from a magnetic material.
 12. Thefluid bearing motor of claim 2 or 5, wherein said fixed shaft is madefrom a magnetic material, the clearance between the first steppedsurface and the second stepped surface is filled with magnetic fluid,and a magnet is disposed at the inner periphery of said hollow cylinderat the chassis side rather than the projection.
 13. The fluid bearingmotor of claim 12, wherein said stop ring is made from a magneticmaterial.
 14. A fluid bearing motor according to claim 1, wherein: saidfixed bearing member comprises a first inner periphery and a secondinner periphery, the first inner periphery is smaller in diameter thanthe second inner periphery, the hollow cylinder is formed with aprojection at a part of its outer periphery, and the projection isarranged in such manner that it is positioned within the diameter of thesecond inner periphery of the fixed bearing member and outside the firstinner periphery.
 15. The fluid bearing motor of claim 14, wherein saidprojection is formed of a circular stop ring.
 16. The fluid bearingmotor of claim 14, wherein a dynamic pressure generating groove isformed in at least one of the first inner periphery and the outerperiphery of the hollow cylinder; the upper end of the fixed sidebearing and the lower end of the flange are opposed to each other with apredetermined clearance provided therebetween; a dynamic pressuregenerating groove is formed in at least one of the upper end surface ofthe fixed side bearing and the lower end surface of the flange; and thehydrodynamic lubricant is filled (i) between the first inner peripheryand the outer periphery of the hollow cylinder, (ii) between the upperend of the fixed side bearing and the lower end of the flange, and (iii)between the first stepped surface and the second stepped surface. 17.The fluid bearing motor of claim 14, wherein the hollow cylinder and theflange are integrally formed from same material.
 18. The fluid bearingmotor of claim 14, 15, or 16, wherein the stop ring is made from a resinmaterial having low friction characteristics.
 19. The fluid bearingmotor of claim 14, 15, or 16, further comprising a permanent magnetfixed on the chassis, opposing to the other surface of the stop ringwith a clearance provided therebetween, wherein the fixed side bearingis formed from a magnetic material.
 20. The fluid bearing motor of claim14, 15, or 16, further comprising a permanent magnet fixed on the othersurface of the stop ring, wherein the fixed side bearing is formed froma magnetic material.
 21. The fluid bearing motor of claim 19, whereinthe stop ring is formed from a magnetic material.
 22. The fluid bearingmotor of claim 20, wherein the stop ring is formed from a magneticmaterial.
 23. The fluid bearing motor of claim 14, 15, 16, or 17,wherein the predetermined clearance between the stepped surface and theother surface of the stop ring ranges from 5 μm to 100 μm.
 24. The fluidbearing motor of claim 14, 15, 16, or 17, wherein the chassis has apositioning projection for positioning the fixed side bearing.
 25. Thefluid bearing motor of claim 24, wherein the positioning projection isring-form, and the outer periphery of the fixed side bearing engages theinner periphery of the positioning projection.
 26. The fluid bearingmotor of claim 25, wherein the positioning projections are at leastthree columnar projections which externally come in contact with theouter periphery of the fixed side bearing.